This book is good at what it is. The problem may come from understanding exactly what it is, especially from the Amazon listing.
It is "more than a fakebook." But it's only *slightly* more than a fakebook.
It includes 55 compositions by Mingus. For each it contains a lead sheet, and for almost all, a short anecdote, ranging from one to four paragraphs. For some compositions, it includes arrangements across several instruments for the head of the tune - but only where the arrangements are distinctive for the tune. It includes some reproductions of lead sheets in Mingus' own hand, alongside typeset sheets. The reproductions are interesting in how messy they are, but otherwise really hard to read. And the book includes a number of photographs, and a few other random pieces that are of some interest - a biography, and a couple of essays.
The book is focussed entirely on Mingus as a composer, not as a bassist.
Treat it as a book of lead sheets of Mingus' compositions, and you will not be disappointed.
What this doesn't do is look at Mingus as a bassist at all. There are no transcriptions of Mingus' solos. There is no discussion of his bass playing technique. In most of the lead sheets there is not a bass clef at all. In a few arrangements there are bass clefs for baritone sax and trombone, and in only a very few places, for a written double bass line.
So, overall, this is great if you are interested in Mingus as a composer. It is not very useful if you are interested in Mingus as a bassist.